Anti-scatter grids show various performances depending on the complicated design parameters. However, it takes long time and cost to fabricate grids and perform experiments to evaluate the performance of grids. Therefore, to replace actual measurements, we performed Monte Carlo simulation study and obtained Tp (transmission of primary radiation) and Tt (transmission of total radiation) values which represent grid performance. Beam quality check was done to validate our simulation results. Although the simulation lowers the cost, it is still time consuming work. To solve those problems, empirical formulae for Tp and Tt were derived by analyzing the results of the simulation. Design parameters for grids were setup in order to derive the empirical formulae. The derived empirical formulae helped us estimate Tp and Tt values of an arbitrary grid without a complicated experiment or a tedious simulation, and easily obtain contrast improvement factor (CIF) and Bucky factor (BF) which are commonly used to evaluate the performance of a grid. The design parameters of a grid for the minimum patient's dose can be proposed with maintaining the image quality within the designable range using the derived empirical formulae.